Exhaust gas driven turbochargers include a rotating shaft carrying a turbine wheel and a compressor wheel, which is rotatably supported within a center housing by one or more lubricated bearings (e.g., oil lubricated). The turbine wheel is driven by the exhaust gas at high rotational speeds, often well in excess of 100,000 RPM, to drive the compressor wheel to provide boosted charge air for use by an internal combustion engine.
With respect to lubrication of various bearing surfaces, one approach relies on two distinct lubricant galleries machined in a turbocharger center housing that allow lubricant to flow to radial bearing journals. While this approach provides for reasonable bearing power losses, production issues exist related to machining, deburring, cleaning and quality control of the center housing. Another approach relies on a single lubricant gallery machined in a turbocharger center housing. The single gallery allows lubricant to flow to radial bearing outer journals and bore journals where flow is outward toward the bearing ends only.
The latter single gallery approach is reasonably low cost with respect to machining and related processes for production of the center housing but the bearing power losses are can be high.
A need exists for technology that strikes an appropriate balance between production related costs and performance. As described herein, various exemplary technologies aim to address this need and others needs.